Changes in pupil dilation and P300 amplitude indicate the possible involvement of the locus coeruleus-norepinephrine (LC-NE) system in psychological flow

Psychological flow is a state of full task immersion. The present study was conducted to test the hypothesis that psychological flow is positively related to activity of the phasic locus coeruleus-norepinephrine (LC-NE) system, which supports decisions on whether to engage in or disengage from the current activity. Subjective flow was assessed among 36 participants who engaged in a gamified version of the n-back task with various difficulty levels (0, 1, 2, and 3 back). During the tasks, continuous pupil diameter and EEG were recorded. We found that psychological flow and two presumed indicators of the phasic LC-NE activity (pupil dilation and EEG P300 amplitude) fit inverted U-shapes with increasing subjective task difficulty. Moreover, a positive linear relationship between psychological flow and pupil dilation (not with P300) was found. In conclusion, this study indicates the involvement of the LC-NE system in the peak experience of flow.


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The relationship between objective task difficulty and EEG P300 amplitude failed to fit the quadratic model. D)

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The relationship between the subjective task difficulty and EEG P300 amplitude failed to fit the quadratic model.

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The means  standard errors are shown. Below, we present the P300 amplitude related results of the data after removing the 0-back 46 task. Note: After removing the 0-back task, only one data point was left in the 'much lower than 47 my skill' group'. This confirms that in line with our initial design, the 0-back was considered the 48 easiest task. The 1-back task was already considered relatively challenging. 49 2.1 P300 amplitude changes across different task difficulties after removing 0-back task 50 The relationship between P300 and objective task difficulty fit a linear rather than quadratic Conditional R 2 =0.746, Marginal R 2 = 0.086), see Fig. S4B. 57 58 Fig. S4| A) The relationship between objective task difficulty and EEG P300 amplitude (removed 0-back task) 59 fit a negative linear trend. B) The relationship between the subjective task difficulty and EEG P300 amplitude 60 (removed 0-back task) fit a negative linear trend. The means  standard errors are shown. B = 0.013, Conditional R 2 =0.661, Marginal R 2 = 0.007), see Fig. S5. 64

Fig. S5|
The relationship between P300 and flow (0-back task removed) failed to fit a linear trend.
Overall, 13 participants practiced the task for two rounds (one round equals to 20 trials * 4 69 blocks), 22 participants practiced the task for one round, and two participants requested to skip the 70 practice halfway of their second round of practice (practiced 92 trials and 100 trials separately). 71 We checked the relationship between the number of practice trials and pupil dilation and 72 p300 amplitude. The results show that there was no relationship between the amount of practice

Performance Results 78
Descriptive information of performance (correct rate, d-prime and reaction time) in 79 objective and subjective task difficulty groups are shown in Fig. S6.

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We tested the relationship between flow and task performance by regressing flow on the 84 d-prime in a mixed effect model and added objective task difficulty as a control variable. The result 85 suggested that there was a positive relationship between flow and task performance ((flow) = 0.105,

Measures of flow 89
In addition to the two general flow items, participants were also asked to report nine 90 psychological aspects that assumed to co-occur with flow --here we referred to flow characteristics. 91 Items are adapted from the short flow state scale (Jackson, Martin, & Eklund, 2008). They are 1) 92 Competence: "I feel I am competent enough to meet the high demands of the situation"; 2) 93 Automaticity: "I did things spontaneously and automatically without having to think"; 3) Goal 94 clarity: "I had a strong sense of what I wanted to do"; 4) Performance awareness (or feedback): "I 95 had a good idea about how well I was doing while I was involved in the task"; 5) Focus: "I was 96 completely focused on the task at hand"; 6) Control: "I had a feeling of total control over what I 97 was doing"; 7) Little self-referential thinking: " I was not worried about what others may have 98 been thinking of me"; 8) Distorted time perception: "The way time passed seemed to be different 99 from normal"; 9) Rewarding (or autotelic property): "I found the experience extremely rewarding". 100 Participants answered along a 5-point Likert scale from "1=strongly disagree" to "5=strongly 101 agree".          We then explored the factor structure of the combined 11 flow-relevant subjective 129 measures by conducting factor analysis with principal components (component extracted based on 130 Eigenvalues greater than 1) and Varimax rotation methods for each task. We find that in the four 131 tasks, the two general flow items always loaded into the first component extracted from all items 132 while loading situations for the other 9 items was inconsistent. See Table S4 for summarized factor 133 loading information. 134 To further explore the relationship between different flow characteristics and general flow 135 state induced by our experiment, linear mixed models with random intercepts were ran separately.

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Comparisons of pupil dilation in four n-back conditions. C) Comparisons of p300 amplitude in four n-back conditions. 196 D) Mean score of flow in different subjective task difficulty groups. E) Mean score of pupil dilation in different 197 subjective task difficulty groups. F) Mean score of P300 amplitude in different subjective task difficulty groups.

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The means  standard errors are shown.